AWWA PATH56530

Escherichia coli is a gram-negative bacillus belonging to the Enterobacteriaceae and is the indicator organism by excellence of water quality. In fact, the need for more rapid, specific and sensitive tests is essential in the water industry. Thus the importance of giving rapid and accurate results on water quality is high. Several rapid methods for detection of E. coli have been proposed. This study compares the membrane filtration method using the culture medium Membrane Lauryl Sulphate Agar (MLSA) that was incubated at (44+/-0.5)C for (21+/-3) hours followed by confirmation with DEV-fluorocult incubated at (44+/-0.5)C for (21+/-3) hours with Colilert-18. incubated at (36+/-2)C for 18 hours. The two methods are selective for E. coli but based on different characteristics, namely capacity of hydrolyze lactose and the presence of the enzyme beta-D-glucuronidase, respectively. Water samples were analyzed from the surface water source Tejo River, Castelo do Bode reservoir and Olhos d'¿gua, a groundwater source since September 2001, using both methods. Samples from collaborative trials were also analyzed by both methods. The comparison of results was made according to ISO/DIS 17994. The data collected was sufficient to demonstrate using a standard one-sided evaluation that the alternative method (Colilert-18.) has a higher recovery than the reference method (LO=2.90>0). Includes 3 references, figures.